As is well known, a neural implant includes a sealed package portion with an electronic component (or an electronic module) built therein and an electrode portion configured to interface with nervous tissue and input or output a signal to or from an electronic component. The electrode portion that interfaces with nerves generally has a multi-channel electrode site and interacts with a nerve cell or tissue to transfer electrostimulation or to measure various micro bio-signals caused by nervous tissue after being inserted into a human body.
In the case of a conventional neural implant, an electrode is manufactured based on a micro metal (for example, Pt:Ir (90:10) alloy and the like) wire and a sealed package is realized using a titanium package, a ceramic insulator, and a platinum feedthrough.
However, since such conventional neural implants are manually manufactured and need a high skill level in manufacturing an electrode and a complicated packaging process, manufacturing costs increase and a yield is low.
To overcome such limitations, a liquid crystal polymer-based neural implant in which a multi-channel electrode portion is manufactured using a semiconductor process and a sealed package is realized using only a simple thermocompression process has been provided. Since a liquid crystal polymer has water permeability and gas permeability significantly lower than those of existing biocompatible polymers such as polyimide, parylene-C and the like, a lifespan of a polymer-based neural implant may be greatly increased.
FIGS. 1a to 1d are process flow diagrams illustrating main processes of manufacturing a liquid crystal polymer-based neural electrode according to a conventional method.
Referring to FIG. 1a, an electrode material 104a is having a thickness of several hundred nm is stacked on a high temperature liquid crystal polymer substrate 102 (with a melting point of 310 degrees) by performing an evaporation or sputtering process.
Subsequently, a photoresist material is applied thereto and a photolithography process and the like are performed, thereby forming, for example, a photoresist pattern 106 having an arbitrary pattern on the electrode material 104a as shown in FIG. 1b. 
Next, an etching process (for example, a wet etching process) with the photoresist pattern 106 as an etching barrier layer is performed and then a residual photoresist pattern is removed (stripped), thereby forming, for example, an electrode 104 having an arbitrary pattern as shown in FIG. 1c. 
Afterward, since a thermocompression process is performed using a heating press and the like, for example, as shown in FIG. 1d, a liquid crystal polymer cover layer with a site window 108 formed therein is adhered to a front surface of the liquid crystal polymer substrate 102 with the electrode 104 formed therein. Here, the site window 108 that exposes a top of the electrode 104 may be defined as an electrode site.
However, in a conventional method of manufacturing a micro neural electrode, when high pressure is applied during a thermocompression process for combining a liquid crystal polymer cover layer, for example, disconnection in which a metal pattern (a lead wire) breaks due to a thin conductor as shown as 202 in FIG. 2 occurs. To prevent such disconnection, it may be considered to lower thermocompression pressure. However, in this case, since adequate pressure is not transferred between a liquid crystal polymer substrate and a cover layer, adhesion between layers is decreased.
Also, in the case of a conventional micro neural electrode, an electrode site (a part in which a metal is exposed to interface with a nerve cell) at a liquid crystal polymer-based electrode is formed by making a hole corresponding to a site window at a liquid crystal polymer cover layer using a laser in advance and a liquid crystal polymer substrate and a cover layer are aligned and stacked using a metal pin and then adhered through thermocompression. In this case, for example, as shown in FIG. 3, the hole made in advance may become narrower or blocked as the cover layer is melted during the thermocompression process.
Additionally, in the conventional method of manufacturing a micro neural electrode, the minimum thickness of a liquid crystal polymer film in commercial use is limited to 25 μm and the minimum thickness of an electrode manufacturable when a substrate and a cover layer are thermally compressed is limited to 50 μm. Due to the limitations of thickness, it is difficult to realize an electrode with high flexibility (for example, an electrode that is inserted into a retina).
Also, since a liquid crystal polymer film having a thickness of several tens of μm has inferior optical characteristics (for example, permeability and the like), it is impossible to integrate an optical sensor that needs high resolution (a photodiode and the like) inside a sealed package.
Also, in the case of a liquid crystal polymer-based electrode, various processes are performed on a liquid crystal polymer film attached to a wafer and finally an outline is cut through laser cutting. For example, as shown in FIG. 4, due to an alignment error of laser equipment for laser cutting, a metal pattern of a lead wire (an internal connection line) 402 and the like may be cut out. In FIG. 4, 404, which is an unmentioned reference number, refers to an electrode site.
To prevent such problems, since it is necessary to cut with a margin at or above an alignment error, it is difficult to manufacture micro sized electrodes due to this.
Also, in the conventional method of manufacturing a micro neural electrode, since a liquid crystal polymer film is simply positioned above and below a circuit with an electronic component attached thereto and then thermocompression is performed while a sealed package portion is packaged, excessive pressure is applied to the electronic component in such a way that a risk of disconnection, short circuit, or a failure of the component may be present. Also, since uniform pressure is not transferred between liquid crystal polymer films, a crease and the like is generated in such a way that not only aesthetics may be spoiled but also sealability decreases. Such problems may become more severe in that case of a sealed package that needs a curved surface, for example, an artificial retina attachable to an eyeball.